1. Field:
This invention relates to the field of radiant coolers and specifically for improved radiation shielding systems for such radiant coolers.
2. Prior Art:
The radiation shielding system of this invention is utilized to replace a multi-layer insulation blanket. Passive radiation coolers have been known in the past which utilize multi-layer insulation blanket systems much in the same fashion as such have been utilized in cryogenic applications. The utilization of multi-layer systems known in the prior art is disclosed in the following references: "Multiple Layer Insulation for Cryogenic Applications" (R. H. Kropschot, Cryogenics, March 1961, P. 171) and "Effective Thermal Insulation Multilayer Systems" (P. E. Glaser, Cryogenic Engineering News, April 1969, p. 16). A similar review is given by Kropschot in Chapter 6 of Applied Cryogenic Engineering (ed. by R. V. Vance and W. M. Duke, Wiley, 1962).
Multilayer insulation blanket systems achieve large, 100 or greater, insulation factors when the end and penetration effects are small. This is generally the case when the scale is large or the insulated volume forms a closed surface. For example, degrading effects are small in an insulation blanket for a space craft or for large cryogenic storage containers. When applied to passive radiant coolers, however, the multilayer insulation blanket necessarily does not cover a closed volume, the scale is relatively small and the end effects are significant.
The multilayer blankets used in radiant coolers associated with space satellites usually consists of sheets of polyester aluminized on both sides and separated by one or two layers of low conductivity silk or polyester mesh. In some insulations there is no low conductivity separation. Instead the aluminized reflectors are kept apart by distorting the reflecting surfaces to obtain only point contacts between the layers.
It has been found in practice that multilayer blankets are degraded by their open end areas, which of course increases with the number of layers, by penetrations with supports for the blanket and by compression of the layers. While such systems have measured insulation factors in the range of 60 to 80 and, while it may be possible to reach an insulation factor of 100, it is highly unlikely in view of the drawbacks to such devices that they can be effective to achieve insulation factors as high as 100.
In addition there are significant outgassing and contamination problems which may result in degradation of such systems' performance.